0001342: project files including captions, once saved with 2.13.38, can not be reloaded into the same version

Description

When trying to load a metadata.xml containing either OCAP or CCAP created with 2.13.38, the same version of DCP-o-matic crashes/vanishes silently. Either something in the project metadata file creation, or interpretation, I guess.

Also, when loading a metadata.xml file from an earlier version that includes timed text (e.g. srt), the project can not be loaded (see screenshot).

2.13.38, OS X Sierra.

As 2.12.x can not load 2.13.38 project files, there is probably urgent need to fix this.
Can we create 'some' backwards compatibility for the new functions in 2.12.9? Like interpreting all captions as plain subtitles upon load?

project files including captions, once save with 2.13.38, can not be reloaded into the same version => project files including captions, once saved with 2.13.38, can not be reloaded into the same version